The invention is directed to an electrolytic palladium bath containing palladium sulfite and an acid. Such baths serve for the deposition of glossy, flaw free, and low tension palladium coatings for industrial and decorative uses. In the electrical art, palladium coatings are used on contact material; in the decorative industry, they are frequently employed as a replacement for white gold.
The known ammoniacal palladium baths have not been proved practical since, because of the vaporization of ammonia and the sensitivity to impurities, there cannot be maintained constant operating conditions, and the properties of the coatings instead do not satisfy the requirements placed in the art.
Hydrochloric acid baths based on palladium chloride attack a number of base metals during the electrolyzing. Through this, there are not produced sufficiently adhesive coatings, and the palladium frequently deposits in powdery form.
According to German patent No. 2105626, it is possible through the use of palladium nitrate in sulfuric acid solution and through the addition of palladium sulfite to deposit glossy, flaw free, and low tension coatings which fulfill the quality requirements placed in the art.
However, it has now been shown that, in the deposition of the palladium from the palladium nitrate, the nitrate residue can be enriched in the bath as free nitric acid. Through this, a corrosive mixture of sulfuric acid and nitric acid can form which can lead to a corrosion attack with various metals. This impairs the adhesiveness of the palladium coatings. Therefore, it was the problem of the present invention to find an electrolytic, palladium bath containing palladium sulfite and an acid which yields coatings which satisfy the requirements of the art and does not act corrosively on the base metal.